1. Field of the Invention
The present invention relates to a phosphoric acid-type fuel cell comprising a pair of gas-diffusion electrodes and a porous matrix retaining phosphoric acid as an electrolyte (hereinafter referred to as phosphoric acid electrolyte-retaining matrix).
Particularly, the present invention relates to an electrolyte-retaining matrix and a process for producing the matrix.
2. Description of the Prior Art
As phosphoric acid electrolyte-retaining matrix, there has been used a phenolic resin fiber cloth or nonwoven fabric or a mixture of silicon carbide powder and polytetrafluoroethylene (an organic binder).
These matrices are described in detail in the specification of U.S. Pat. No. 4,017,664. According to the disclosure of the specification of U.S. Pat. No. 4,017,664, phosphoric acid reacts with phenolic resin at a temperature of above 250.degree. F. (about 121.degree. C.) in the phenolic resin-type matrix. By this reaction, molecules which are adsorbed on the electrode catalyst causing deterioration of the activity of the catalyst are formed, whereby the performance of the fuel cell is deteriorated. For preventing the reaction of phosphoric acid with the phenolic resin, it is effective to lower the operating temperature of the cell. However, another problem of serious reduction of output of the cell is posed by the lowering of the working temperature. When a mixture of silicon carbide powder with polytetrafluoroethylene (organic binder) is used as a matrix material, the operating temperature of the fuel cell can be elevated to about 190.degree.-200.degree. C. However, organic binders are generally water-repellent and particularly fluorine resins such as polytetrafluoroethylene has a high water-repellency and no affinity with phosphoric acid. Therefore, the electrolyte-retaining matrix has only a poor phosphoric acid-retaining capacity and the phosphoric acid-retaining capacity thereof is reduced gradually.